At industrial wastewater plants, the Environmental Protection Agency enforces requirements to ensure that operators pretreat pollutants in their wastes to protect local sanitary sewers and wastewater treatment plants. Such extreme wastewater handling environments operate under continual chemical exposure and heavy abrasion that deteriorate concrete and corrode steel in clarifiers, containment pits, anaerobic digesters, manholes, tanks, and other infrastructure assets. Polyurea coatings are proving ideal for rehabilitation.
Concrete Cracking and Deterioration
Various factors can cause these structures to develop sizable cracks, through which wastewater can escape by exfiltration. Cracks can develop in aging concrete wastewater infrastructure for many reasons, including earth movements or daily and seasonal temperature changes that cause expansion and contraction, such as freeze-thaw. Additionally, harsh chemicals used to treat wastewater can deteriorate the concrete, as can exposure to hydrogen sulfide (H2S) gas, a form of sulfuric acid (H2SO4) in sewers created by anaerobic organisms. Groundwater could also enter the wastewater system through infiltration. Leaks, cracks, and damage to existing coating systems top the list of challenges in facility maintenance and new construction and can also trigger severe financial penalties. Since the EPA regulates municipal wastewater and stormwater management, concrete cracks or leaks that lead to wastewater exfiltration or groundwater infiltration can put the municipality in violation of those regulations.
For concrete repairs in wastewater infrastructure from municipal manholes and lift stations to clarifiers, trenches, and sumps. A cement material is traditionally used to repair wastewater-related sewer leaks. But this process has disadvantages, as do other coating materials. Hydrogen sulfide [H2S] gas eats away at the cement in sewer concrete, so it may only have a lifespan of a few years. Polyurethanes have more elongation but nothing like polyurea. Because much lower elongation properties will limit epoxies, they will crack and don't bridge cracks well.
Advanced polyurea coatings and liners are ideal for wastewater infrastructure rehabilitation by delivering strong, flexible, abrasion- and chemical-resistant waterproofing that not only bridges existing cracks but can elongate up to 400% without cracking. The spray-applied waterproof coating creates a seamless, waterproof, durable protective liner that stops leaks and strengthens the integrity of the entire structure. It exhibits superior physical properties such as elongation up to 400%, cracks bridging, hardness, and tensile strength to create a robust industrial liner that protects, strengthens, and waterproofs the infrastructure. Because these systems set and cure rapidly and can be installed and used in many temperatures, they also minimize downtime.
Characteristics of Polyurea
Several of polyurea's characteristics help to extend wastewater infrastructure longevity and prevent wastewater exfiltration and groundwater infiltration.
Since the polyurea system provides superior elongation, it bridges cracks up to 0.125in, with tensile strength higher than traditional materials, it has lower permeability for better waterproofing. Its impact, abrasion, and chemical resistance are flawless, so it resists hydrogen sulfide. Instead of years between replacing cementitious coatings, the polyurea coating can cost-effectively provide decades of protection.
With proper crack repair and surface preparation, the polyurea coating can be a thick film applied directly to the concrete or similar substrate. An alternate application method that can sometimes mitigate the need for surface or crack repairs is to pre-spray the polyurea. Geotextile fabric panels are placed on top of the substrate and fuse the panel edges with more polyurea. Because of the polyurea's ability to set and cure quickly, it also minimizes wastewater treatment plant or infrastructure downtime. This can translate into thousands of dollars in savings per hour, all while avoiding days of service interruption. Since it sets and cures rapidly, structures will be back in service quickly after spraying.
Wider Temperature Range
While traditional coatings such as cementitious, epoxies, and polyurethanes will prematurely fail if not installed under a relatively narrow range of temperatures, the polyurea used by Osborn is designed for installation and use from -40 to 350 deg F (-40 to 176.7 degC). It will withstand decades of freeze-thaw cycling and wide temperature and humidity variations.
Generally, clarifier maintenance crews need to use high-pressure power washers for hours to clean solid waste from concrete surfaces, since the polyurea provides waterproofing and has a cleanable surface, crews can hose down the clarifier to clean it. This can cut the required weekly clarifier cleaning by two-thirds. For wastewater-related rehabilitation, polyurea is a superior coating for any application that requires crack bridging, longevity, chemical and temperature resistance, and fast turnaround, longevity, chemical and temperature resistance, and fast turnaround.